1. Technical Field
The present invention relates to a liquid ejecting apparatus provided with a function for detecting an edge position of a medium, such as a sheet of paper, by an optical sensor provided to a carriage including a liquid ejecting head, and also relates to a sensor sensitivity setting method in a liquid ejecting apparatus.
2. Background Technology
An ink jet printer has been known as this kind of liquid ejecting apparatus. Provided to the printer is a carriage which moves in a direction (main scanning direction) intersecting with a conveyance direction for sheets of paper, and which has a recording head. During printing, ink droplets are ejected from the recording head toward a sheet of paper while the carriage is being moved, whereby an image or the like is printed onto the sheet of paper (for example, Patent Documents 1 to 4, etc.).
In, for example, the printers described in Patent Documents 1 to 3, an optical sensor of a light reflection type (an edge sensor) is provided to the carriage, and a widthwise edge position of the sheet of paper is detected using the optical sensor when the carriage is moved in the main scanning direction. More specifically, a detection value from the optical sensor and a threshold value are compared against each other, and when the detection value changes to being the threshold value or lower or to being the threshold value or higher, the current position is determined to be an edge detection position (edge position) of the sheet of paper.
It has been noted that an ink mist generated when the liquid ejecting head ejects the ink droplets has been present in the vicinity of a movement path of the carriage, as has floating matter such as paper dust generated from the sheet of paper. When the floating matter becomes attached and the optical sensor is sullied, the result is a gradual decline in the amount of light received by the optical sensor, as well as changes in the amount of deviation between the actual edge position of the paper and the edge detection position from when the detection value thereof changes to being the threshold value or lower or to being the threshold value or higher. In order to resolve this, in a printer apparatus described in Patent Reference 1, a threshold value that is optimal for every iteration is re-determined for every iteration of printing, and thus it is possible to detect the edge position with high positional accuracy by using a threshold value that is optimal and has not been impacted even by aging changes in the surface state of a support base nor by aging changes caused by sullying of the optical sensor.
In the printers described in Patent Documents 2 and 3, a rib of a support base and a portion other than the rib (a groove part) are detected by an optical sensor (a recording sheet detection sensor), a detection sensitivity of the optical sensor is determined on the basis of a ratio or difference between respective detection voltages, and a threshold value corresponding to the detection sensitivity is set. For this reason, there will be a constant amount of positional deviation between the edge detection position of when the detection value of the optical sensor crosses over the threshold value and the actual edge position, and thus the edge position can be detected at high positional accuracy when corrected with a constant correction amount corresponding to the amount of positional deviation thereof.
Patent Document 4 discloses a printer having a carriage equipped with a movable shutter for closing an opening of a read sensor provided to the carriage, a means for opening and closing the shutter, and a maintaining means for maintaining the open or closed state. According to this printer, the shutter is closed when the read sensor is not in use, and thus it is possible to avoid sullying of the read sensor by the attachment of floating matter such as the ink mist.
Japanese Laid-open Patent Publication No. 2002-127521 (for example, paragraphs [0037]-[0052], FIG. 4, FIG. 5, etc.) (Patent Document 1), Japanese Laid-open Patent Publication No. 2003-260829 (for example, paragraphs [0053]-[0059], FIG. 5, FIG. 6, etc.) (Patent Document 2), Japanese Laid-open Patent Publication No. 2010-194748 (Patent Document 3), and Japanese Laid-open Patent Publication No. 11-227176 (for example, paragraphs [0023]-[0034], FIGS. 2 to 4) (Patent Document 4) are examples of the related art.